A non-linear feature-domain noise reduction algorithm based on the minimum mean square error (MMSE) criterion on Mel-frequency cepstra (MFCC) has been developed for environment-robust speech recognition, as generally described in U.S. Patent Application Publication No. US2005/0182624 (herein incorporated by reference). While this technology works reasonably well in many situations, like other such speech enhancement algorithms, automatic speech recognition accuracy is improved for noisy speech, but is more degraded with clean speech.
Other problems include that the original speech enhancement algorithm sometimes leads to abrupt change of the gain, and that the parameters in the prior speech enhancement algorithm are manually selected and thus sub-optimal. Any improvements to these problems are desirable.